What was the most important political body in ancient Athens?

The first was the ekklesia, or Assembly, the sovereign governing body of Athens. Any member of the demos--any one of those 40,000 adult male citizens--was welcome to attend the meetings of the ekklesia, which were held 40 times per year in a hillside auditorium west of the Acropolis called the Pnyx.

The City Assembly. Any male free citizen over the age of 18 could join its sessions in the ancient city-state. Women and slaves were excluded. Any member could debate and express opinions.